[3.12] gh-116040: [Enum] fix by-value calls when second value is falsey (GH-116072) (GH-116476)

e.g. Cardinal(1, 0)

(cherry picked from commit 13ffd4bd9f)

Lib/test/test_enum.py

@@ -3312,6 +3312,40 @@ class TestSpecial(unittest.TestCase):
                     member._value_ = Base(value)
                     return member
 
+    def test_second_tuple_item_is_falsey(self):
+        class Cardinal(Enum):
+            RIGHT = (1, 0)
+            UP = (0, 1)
+            LEFT = (-1, 0)
+            DOWN = (0, -1)
+        self.assertIs(Cardinal(1, 0), Cardinal.RIGHT)
+        self.assertIs(Cardinal(-1, 0), Cardinal.LEFT)
+
+    def test_no_members(self):
+        with self.assertRaisesRegex(
+                TypeError,
+                'has no members',
+            ):
+            Enum(7)
+        with self.assertRaisesRegex(
+                TypeError,
+                'has no members',
+            ):
+            Flag(7)
+
+    def test_empty_names(self):
+        for nothing, e_type in (
+                ('', None),
+                ('', int),
+                ([], None),
+                ([], int),
+                ({}, None),
+                ({}, int),
+            ):
+            empty_enum = Enum('empty_enum', nothing, type=e_type)
+            self.assertEqual(len(empty_enum), 0)
+            self.assertRaises(TypeError, 'has no members', empty_enum, 0)
+
 
 class TestOrder(unittest.TestCase):
     "test usage of the `_order_` attribute"